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"Most" officers in the Navy (and Army and Marines) get two promotions if they stay long enough. In the Navy, that would be from Ensign (ENS.) to Lieutenant Junior grade (LTJG.) and then to Lieutenant (LT - the equivalent of an Army or Air Force Captain). That's because the first two officer ranks are basically "trainee" positions, and the last one mentioned is the first level with "real responsibility.
That's where the "weeding out" begins in earnest. Only about half of the Navy Lieutenants/Army Captains make it to the mid level, Lieutenant Commander or Major. If you haven't made it to the next level after that by your late 30s, you're on your way out. Around 40, such people retire early from the service at half pay.
Say someone makes it to Commander/Lieutenant Colonel. There is another weeding out point in the mid-40s. If you survive that round, and get promoted to Captain/Colonel, you can be a "lifer." Very few people make it to "flag" rank (admiral or general of any description), but reaching the aforementioned high officer level will allow someone to stay until normal retirement age in the early 50s. The few flag officers do get to retire later than the early 50s.
Enlisted men have similar, though perhaps less stringent, pressures, than officers. As in the case of officers, the first few levels, "buck" Private, Private Second and First Class, or their naval equivalents, are "trainees." These are the grunts that do the "heavy lifting." Most enlisted men serve two or three years in those ranks as an entry to adulthood, then move on to civilian pursuits. And if you can't, given sufficient time, make it past Private First Class, you probably aren't cut out for the military life anyway.
While most privates leave on their own volition, the weeding out for non-commissioned officers starts at "Corporal," (E4), which is roughly the enlisted men's equivalent of Army "Captain." Such people have supervisory authority (over Privates). Not everyone is cut out to lead others, and the Army doesn't want people stuck at that level.
The next two levels, Sergeant and Staff Sergeant, are perhaps the key ones. because is where the decision making responsibilities start. (Staff Sergeants differ from "plain" Sergeants in the scope of their duties, rather than level of authority.) These levels are perhaps equivalent to Lieutenant Commander and Commander in the Navy officer ranks. Again, there is an "up or out" element to these ranks.
The higher level enlisted ranks, Sergeant First Class, Master Sergeant, and Sergeant Major are the "lifer" ranks, equivalent to Captains and Admirals in the Navy. These ranks are fairly sparsely populated. Here, if you've made it past Staff Sergeant, you are allowed to remain at your "level of incompetence."
It is worth noting that "Officer" and "Enlisted" tracks in the military are similar to "managerial" and "technical" tracks in industry. While officers and managers have more authority than enlisted men and technicians, the senior members of the latter group are actually paid more than the junior members of their nominal supervisors.